Exemplary embodiments of the present invention relate to an image sensing device and a method for operating the same, and more particularly, to an image sensing device that can operate an exact correlated double sampling (CDS) operation and reduce power consumption, and a method for operating the same.
Exemplary embodiments of the present invention relate to an image sensing device, and more particularly, to a circuit for handling an image signal provided from a pixel.
An image sensing device such as a portable camera or a digital camera typically generates images of the world. Examples of a sensing element provided in an image sensing device include a CMOS image sensor and a charge coupled device (CCD) image sensor. A CMOS image sensor or CCD image sensor has a pixel array that respond to light for capturing images.
Each subject in the natural world corresponds to a brightness and wavelengths of light. Each pixel of an image sensor extracts an electrical value from sensing of the brightness and the wavelengths. The electrical value is converted into an electrical voltage that can be processed in the image sensor. An image sensor includes an analog-to-digital (A/D) converter which converts analog voltages sensed by the pixel array into digital values and a memory for use during signal processing.
A pixel array includes a plurality of pixels arranged in a matrix form of columns and of rows. An image sensing device usually processes image data provided from a pixel array with reference to a column. Internal circuits of the image sensing device are designed in terms of the columns of the pixel array.
A data processing unit which processes each column data performs an A/D conversion operation of converting an analog signal into a digital signal, and a CDS operation of removing an offset value. In the CDS operation, a digital value corresponding to an analog value provided from a pixel is calculated, and an offset value included in the digital value is removed.
A counter and a latch corresponding to each column are arranged for converting an analog value into a digital value. Since the counter consumes a relatively large amount of current during operation, the counters consume a large amount of current during data processing.